[Smart Lock, Prefs reconciliation] Prefs migration logic for desktop platforms.

chrome/browser/password_manager/password_manager_setting_migrater_service.h

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CHROME_BROWSER_PASSWORD_MANAGER_PASSWORD_MANAGER_SETTING_MIGRATER_SERVICE_H_
+#define CHROME_BROWSER_PASSWORD_MANAGER_PASSWORD_MANAGER_SETTING_MIGRATER_SERVICE_H_
+
+#include <vector>
+
+#include "base/memory/singleton.h"
+#include "base/prefs/pref_change_registrar.h"
+#include "chrome/browser/prefs/pref_service_syncable_observer.h"
+#include "components/keyed_service/content/browser_context_keyed_service_factory.h"
+#include "components/keyed_service/core/keyed_service.h"
+#include "content/public/browser/notification_observer.h"
+#include "content/public/browser/notification_registrar.h"
+
+class Profile;
+
+namespace sync_driver {
+class SyncService;
+}
+
+// Service that is responsible for reconciling the legacy "Offer to save your
+// web passwords" setting (henceforth denoted 'L', for legacy) with the new
+// "Enable Smart Lock for Passwords" setting (henceforth denoted 'N', for new).
+//
+// It works as follows.
+//
+// Users who are not syncing (this is checked on start-up of the service
+// calling to SyncService:CanSyncStart()) are migrated on a startup of a
+// service. This users can be in following states:
+//   1. N = 0, L = 0
+//   2. N = 1, L = 1
+//   3. N = 1, L = 0
+//
+// Nothing should be done in case 1 and 2 since settings are already in sync;
+// in case 3 we change value of N to 1.

[Nicolas Zea, 2015/09/03 22:44:16]

Doesn't case 3 denote that N's value is already 1?

[melandory, 2015/09/04 15:35:26]

Yep, it should be "we change value of N to 0." Thanks for noticing.

+// The service also observes changes to both preferences, so if one of the
+// preferences is changed locally, then this change is propagated to the other
+// preference.
+//
+// For users who are syncing we save the values for the new and legacy
+// preference on service start up (|inital_values_|) and the values that come
+// from sync during models association step (|sync_data_|). Propagating change
+// of one preference to another preference without having this special treatment
+// will not always work. Here is an example which illustrates possible corner
+// case: the client executes the migration code for the first time, legacy
+// preference has a value equals to 1, new preference was registered for the
+// first time and has default value which is also 1, the sync data snapshot
+// which user has on a client contains new preference equals to 0 and old
+// preference equals to 1, if we blindly propagate these values we first get
+// both preferences equals to 0 after priority pref model was associated and
+// then both preferences equals to 1 after preferences model was associated.
+// But correct final value in this case is 0.
+//
+// On the finish of model association step we derive the new values for both
+// settings using following table (first row contains):
+//
+//  NL*  0_  1_  _0  _1  00  01  10  11

[Nicolas Zea, 2015/09/03 22:44:16]

What are the X and Y axes?

[melandory, 2015/09/04 15:35:26]

Done.

+//
+//  00   00  11  00  11  00  11  11  11
+//  01   x   x   x   x   x   x   x   x  # impossible state
+//  10   x   x   x   x   00  00  00  11
+//  11   00  11  00  11  00  00  00  11
+//
+// The service observes changes to both preferences (e.g. changes from sync,
+// changes from UI) and propagate the change to the other preference if needed.
+//
+// After service is created it waits until Profile and profile related services
+// (such as ProfileSyncService) are initialized and after that observers for
+// the sync state change and preferences changes are registered.
+//
+// Note: componetization of this service currently is impossible, because it
+// depends on PrefServiceSyncable.
+class PasswordManagerSettingMigraterService
+    : public KeyedService,
+      public PrefServiceSyncableObserver,
+      public content::NotificationObserver {
+ public:
+  class Factory : public BrowserContextKeyedServiceFactory {
+   public:
+    static Factory* GetInstance();
+    static PasswordManagerSettingMigraterService* GetForProfile(
+        Profile* profile);
+
+   private:
+    friend struct DefaultSingletonTraits<Factory>;
+    friend class PasswordManagerSettingMigraterServiceTest;
+
+    Factory();
+    ~Factory() override;
+
+    // BrowserContextKeyedServiceFactory:
+    KeyedService* BuildServiceInstanceFor(
+        content::BrowserContext* profile) const override;
+    bool ServiceIsCreatedWithBrowserContext() const override;
+  };
+
+  explicit PasswordManagerSettingMigraterService(Profile* profile);
+  ~PasswordManagerSettingMigraterService() override;
+
+  void Shutdown() override;
+
+  // PrefServiceSyncableObserver:
+  void OnIsSyncingChanged() override;
+
+  // content::NotificationObserver:
+  void Observe(int type,
+               const content::NotificationSource& source,
+               const content::NotificationDetails& details) override;
+
+ private:
+  // Initializes the observers: preferences observers and sync status observers.
+  void InitObservers();
+
+  // Called when the value of the |kCredentialsEnableService| preference
+  // changes, and updates the value of |kPasswordManagerSavingEnabled|
+  // preference accordingly.
+  void OnCredentialsEnableServicePrefChanged(
+      const std::string& changed_pref_name);
+
+  // Called when the value of the |kPasswordManagerSavingEnabled| preference
+  // changes, and updates the value of |kCredentialsEnableService| preference
+  // accordingly.
+  void OnPasswordManagerSavingEnabledPrefChanged(
+      const std::string& changed_pref_name);
+
+  // Turns off one pref if another pref is off.
+  void MigrateOffState(PrefService* prefs);
+
+  // Performs a migration after sync associates models. Migration is performed
+  // based on initial values for both preferences and values received from
+  // sync.
+  void MigrateAfterModelAssociation(PrefService* prefs);
+
+  Profile* const profile_;
+  sync_driver::SyncService* sync_service_;
+  PrefChangeRegistrar pref_change_registrar_;
+
+  // Used to register for notification that profile creation is complete.
+  content::NotificationRegistrar registrar_;
+
+  std::vector<bool> initial_values_;
+
+  // Contains values which has came from sync during model association step.
+  // After both preferences data types are associated, new value for the both
+  // preferences will be calculated.
+  std::vector<bool> sync_data_;
+
+  // This vector contains initial value for both preferences. The vector maximum
+  // size is two, where first element is new kCredentialsEnableService
+  // preference and second element is legacy kPasswordManagerSavingEnabled
+  // preference.
+  bool initial_new_pref_value_;
+  bool initial_legacy_pref_value_;
+
+  DISALLOW_COPY_AND_ASSIGN(PasswordManagerSettingMigraterService);
+};
+
+#endif  // CHROME_BROWSER_PASSWORD_MANAGER_PASSWORD_MANAGER_SETTING_MIGRATER_SERVICE_H_